Replacement disc

ABSTRACT

A replacement disc for use between adjacent vertebrae comprising: 
     a body portion having substantially opposing first and second surfaces and being adapted to fit and be held between the adjacent vertebrae; first securement means extending out from the first surface and acting to secure the replacement disc to the first adjacent vertebrae; and second securement means extending out from the second surface and acting to secure the replacement disc to the second adjacent vertebrae.

This application is a continuation of application Ser. No. 361,363,filed June 5, 1989, now abandoned, which is a division of applicationSer. No. 129,302, filed Dec. 7, 1987, now U.S. Pat. No. 4,874,389.

The present invention relates to a replacement disc for use between twoadjacent vertebrae. More particularly, this invention relates to areplacement disc which is held or secured in place between two adjacentvertebrae and acts to take the place of the natural disc material whichhas been removed.

One of human kind's major medical problems involves various difficultieswith the back. In particular, back concerns may involve the vertebraewhich are cushioned by discs which are positioned between the individualvertebrae. Because of exertion, illness, accident or abuse, one or moreof these discs (or at least a portion of the disc material making up thediscs) may become ruptured or is otherwise damaged and requires removal.For example, if a disc is ruptured, at least a portion of the discmaterial may be forced into contact with the spinal cord and/or othersensitive nerves. This contact causes excruciating pain which makes itadvantageous to alleviate this condition by removing the disc material.

The ruptured disc may be surgically removed. Conventional practice hasbeen to fuse together the vertebrae from between which the disc isremoved. However, such fusing can cause a lack of flexibility in theback, especially if more than one pair of vertebrae are to be fused. Itwould be advantageous to provide an apparatus which can be used in placeof the removed natural disc, e.g., so that fusing together of thevertebrae is not necessary.

Therefore, one object of the present invention is to provide areplacement disc for use between adjacent vertebrae. Other objects andadvantages of the present invention will become apparent hereinafter.

A replacement disc for use between adjacent vertebrae to replace naturaldisc material, e.g., which has been removed, has been discovered. In onebroad embodiment, the present replacement disc comprises an outerportion and an inner portion substantially completely surrounded by theouter portion. The inner portion is constructed of a softer, i.e., moreflexible, material than the outer portion. In this embodiment, thereplacement disc is sized and shaped to fit and be held between theadjacent vertebrae. Preferably, the natural tendency of the vertebrae tomove toward each other, e.g., caused by the action of muscles, ligamentsand the like, is sufficient to at least aid in holding the replacementdisc in place between the vertebrae. In order to insure that thereplacement disc is held in place, the two adjacent vertebrae may belinked together, e.g., wired and/or fused together. More preferably, thenatural tendency noted above is sufficient to act as at least theprimary or major means, still more preferably substantially the solemeans, by which the replacement disc is held in place between thevertebrae.

Another embodiment of the present replacement disc is useful when it isdesired to positively secure the replacement disc in place between thevertebrae. Broadly, this replacement disc comprises a body portionhaving substantially opposing first and second surfaces and beingadapted to fit and be held between adjacent vertebrae; and first andsecond securement means. The first securement means extends out from thefirst surface of the body portion and acts to secure the replacementdisc to one of the adjacent vertebrae. The second securement meansextends out from the second surface of the body portion and acts tosecure the replacement disc to the other of the adjacent vertebrae.

The present invention provides substantial advantages. For example, thepresent replacement discs allow injured natural disc material to beremoved without necessitating vertebrae fusion. The replacement discfunctions in much the same manner as does the natural disc material.Thus, the patient is relieved of the pain caused by the injured naturaldisc, while maintaining a substantial amount of the flexibility andfreedom of action which existed prior to the natural disc becominginjured. In addition, as will be discussed in detail hereinafter, thepresent replacement discs can be structured to fit the particularpatient involved.

In the embodiments of the present invention which include an innerportion and an outer portion, both portions are preferably made ofpolymeric material or materials. In any event, the material or materialsof construction should be biocompatible and substantially chemicallyinert and insoluble in the environment in which the replacement disc isutilized. The outer portion of the replacement disc is more preferablymade of silicone elastomer, in particular silastic elastomer. The innerportion is softer than the outer portion and may be made of the same ora different material as is the outer portion. For example, the innerportion may be made of a flexible (as opposed to rigid) polymeric foamor other flexible polymeric material. As used herein, the term "softer"as applied to the inner portion refers to the inner portion being moreflexible or more compressible than the outer portion.

The replacement discs of the present invention which include securementmeans may include a body portion which has an inner portion and an outerportion, or the body portion may be substantially uniform throughout.

The material or materials of construction of the body portion should bebiocompatible and substantially chemically inert and insoluble in theenvironment in which the replacement disc is utilized. If the bodyportion is substantially uniform and/or made of a single material ofconstruction, the body portion preferably comprises silicone elastomer,in particular silastic elastomer.

The first and second securement means extend out from the first andsecond surfaces, respectively, of the body portion and act to secure thereplacement disc to the first and second adjacent vertebrae,respectively. In one embodiment, each of the first and second securementmeans comprises a threaded member. In a particularly useful embodiment,the threaded member of the first securement means is threaded in theopposite direction relative to the threaded member of the secondsecurement means. Such opposite direction threading allows the threadedmembers of both the first and second securement means to be threadedinto both adjacent vertebrae simultaneously. This reduces the amount ofmanipulation required to properly set the replacement disc in place sothat the body portion is fit and held between the adjacent vertebrae.

Preferably, each of the threaded members is tapered toward the end ofthe threaded member away from the body portion. The end of the threadedmember away from the body portion preferably includes a substantiallyflat end surface. The surface area of the end of the threaded memberaway from the body portion is in the range of about 30% to about 60% ofthe surface area of the threaded member at the surface of the bodyportion.

The first and second securement means preferably include a first baseand a second base, respectively, each of which is located in the bodyportion. Such bases act to secure or anchor the securement means to thebody portion. Although the first and second bases can be separatecomponents, in one embodiment the first base and second base are partsof the same component. Such embodiment is particularly useful if it isdesired to have a replacement disc of increased stiffness or reducedflexibility.

In one embodiment, the first base and the second base each extend in thebody portion radially from the longitudinal axis of the first and secondsecurement means, respectively. This radial extension feature moreeffectively anchors or secures the base means and securement means tothe body portion.

Each of the securement means should be made of material or materialswhich are biocompatible and substantially inert and insoluble in theenvironment in which they are to be utilized. In one particularly usefulembodiment, the securement means are made of metal, such as stainlesssteel.

The first and second securement means can be linked together, inparticular by inter-engaging loop segments. Thus, for example, the basesof the first and second securement means can each terminate in a loop,which loops are linked together inside the body portion. Suchinter-engaged loops provide added stability to the replacement disc andprovide for increased coordination between the two adjacent vertebrae.This structure is more rigid because of the inter-engaging loop members.However, it is not as rigid as the structure in which both the firstbase and the second base are parts of the same component.

As can be seen from the above, the present replacement disc system canbe adjusted to take into account the activity level of the medicalpatient in whom the disc is to be used. For example, if such patient isto, or can be expected to, engage in heavy duty activities which putsubstantial strain on the back or vertebrae, a system in which the firstand second base means are parts of the same component or in which thefirst and second base means are linked together by inter-engaging loopscan be used. If no heavy duty activity is anticipated, the system can beconfigured so that the first and second base means are entirelyseparated. Also, if only mild or very light activity is anticipated orif the vertebrae themselves are in such condition so that the securementmeans cannot be effectively utilized, a replacement disc without thesecurement means can be employed. Clearly the present replacement discsystem can be adapted to meet a substantial variety of applications.

These and other aspects and advantages of the present invention are setforth in the following detailed description and claims particularly whenconsidered in conjunction with the accompanying drawings in which likeparts bear like reference numerals.

FIG. 1 is a side view, partially in cross section, of one embodiment ofthe present replacement disc.

FIG. 2 is a side view, partly in cross section, of another embodiment ofthe present replacement disc.

FIG. 3 is a side view, partly in cross section, of a still furtherembodiment of the present replacement disc.

FIG. 4 is a side view, in cross section, of yet another embodiment ofthe present replacement disc.

Referring now to FIG. 1, a replacement disc, shown generally at 10,includes a body 12 shaped in the form of a natural disc which is presentbetween adjacent vertebrae, a first threaded member 14 which extends outof the first surface 16 of body 12, and a second threaded member 18which extends out of a second surface 20 of body 12. First threadedmember 14 is oppositely threaded relative to second threaded member 18.

First threaded member 14 includes a first radially extending member 22,while second threaded member 18 includes a second radially extendingmember 24. In addition, first threaded member 14 includes a first baseelement 26 while second threaded member 18 includes a second baseelement 28. Each of the radially extending members 22 and 24 and thebase elements 26 and 28 are located within the body 12 and help toanchor or secure the threaded members 14 and 18 to the body 12. Thesurface area of the end of each of the threaded members 14 and 18 awayfrom body 12 is equal to about 50% of the crosssectional area of suchmembers at the point where they emerge from body 12.

Body 12 is made of silastic elastomer, and all the other componentsnoted above are made of stainless steel.

Replacement disc 10 functions as follows.

In a surgical operation, in which two adjacent vertebrae are separated,the natural disc material which is injured or otherwise requires removalis removed. One particularly useful implement for separating adjacentvertebrae is described in applicant's co-pending U.S. patent applicationSer. No. 943,481, filed Dec. 19, 1986, which is incorporated in itsentirety herein by reference.

Once the natural disc material is removed, securement holes are drilledinto each of the adjacent vertebrae. Such holes are shaped and sized toaccommodate first threaded member 14 and second threaded member 18respectively. After such holes have been drilled, the replacement discis placed in the space previously occupied by the natural disc material,with the first threaded member being situated in association with one ofthe drilled holes and the second threaded member 18 being located inassociation with the second of the drilled holes. As the two vertebraeare brought back together, the body 12 is turned so as to urge each ofthe first threaded member 14 and second threaded member 18 into thedrilled holes. After the threaded members are secured in the drilledholes, replacement disc 10 acts as the disc material between the twoadjacent vertebrae.

FIG. 2 shows an alternate replacement disc 110 which includes many ofthe same components set forth in replacement disc 10. Except asexpressly noted below, the components and functioning of alternatereplacement disc 110 are substantially similar to the correspondingcomponents and functions of replacement disc 10. For convenience,corresponding components of alternate replacement disc 110 areidentified by reference numerals increased by 100 relative to thecorresponding components of replacement disc 10.

Alternate replacement disc 110 includes a first loop 32 which is securedto and depends from first base element 126 and a second loop element 34which is secured to and depends from second base element 128. First loop32 and second loop 34' are inter-engaged or linked together. Suchinter-engagement or linking together provides for increased stability inalternate replacement disc 110.

FIG. 3 shows a replacement disc 210 which includes many of the samecomponents set forth in replacement disc 10. Except as expressly notedbelow, the components and functioning of replacement disc 210 aresubstantially similar to the corresponding components and functions ofreplacement disc 10. For convenience, corresponding components ofalternate disc 210 are identified by reference numerals increased by 200relative to the components of replacement disc 10.

Replacement disc 210 is structured so that the first threaded member 214extends via a first base extension 36 into the body 212 and is joined bya second base extension 38 of second threaded member 218. A singlecombined radially extending member 40 is associated with both first baseextension 36 and second base extension 38. Body 212 is made of silasticelastomer while the remaining components of replacement disc 210 are ofstainless steel. This type of structure, which may be termed a unitaryreplacement disc, provides substantial rigidity to the replacement disc210. Replacement disc 210 is of particular usefulness where a stiffarrangement between the two adjacent vertebrae is desired, for example,in situations where heavy duty activity is anticipated.

FIG. 4 shows yet another embodiment of the present replacement disc,shown generally at 310. Replacement disc 310 includes an outer portion42 and an inner portion 44, which is completely surrounded by outerportion 42. Replacement disc 310 is shaped in the form of a natural discwhich is present between adjacent vertebrae. Outer portion 38 is made ofa silastic elastomer whereas inner portion 40 is made of a softer,flexible foamed polyethylene. Replacement disc 310 does not include thethreaded members or associated components identified in the previousembodiments.

Replacement disc 310 is placed into the space previously occupied by thenaturally occurring disc material after the adjacent vertebrae areseparated. Once replacement disc 310 is so placed, the adjacentvertebrae are allowed to come together. Once the vertebrae are back intheir normal position, the replacement disc 310 is held between thevertebrae by natural forces. The vertebrae can be wired or fusedtogether to hold replacement disc 310 securely in place. Suchreplacement disc 310 is particularly useful where only light activity isanticipated after insertion of replacement disc 310. The otherreplacement discs identified above are more useful where the patient isexpected to engage in heavier activity.

The components listed in each of the embodiments noted above can, forthe most part, be interchanged with components in the other embodiments.For example, the embodiments shown in FIGS. 1, 2 and 3 can employ a bodywhich includes both an outer portion and an inner portion as set forthin FIG. 4.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. A replacement disc for use between adjacentvertebrae comprising:an outer portion; and an inner portionsubstantially completely surrounded by said outer portion, said innerportion being made of a flexible foamed polyethylene and being softerthan said outer portion, said replacement disc being sized and shaped tofit the be held between said adjacent vertebrae.
 2. The replacement discof claim 1 wherein both said outer portion and said inner portion aremade of polymeric material.
 3. The replacement disc of claim 2 whereinsaid outer portion is made of silicone elastomer.
 4. The replacement ofdisc of claim 2 wherein said outer portion is made of silasticelastomer.
 5. A replacement disc for use between adjacent vertebraecomprising:an outer portion; and an inner portion substantiallycompletely surrounded by said outer portion, said inner portionconsisting essentially of a solid foamed material and being softer thansaid outer portion, said replacement disc being shaped in substantiallythe form of a natural disc which is normally present between saidadjacent vertebrae, and being located between said adjacent vertebrae.6. The replacement disc of claim 5 wherein both said outer portion andsaid inner portion are made of polymeric material.
 7. The replacementdisc of claim 6 wherein said outer portion is made of siliconeelastomer.
 8. The replacement disc of claim 6 wherein said outer portionis made of silastic elastomer.
 9. The replacement disc of claim 5wherein said inner portion is made of a polymeric foamed material. 10.The replacement disc of claim 6 wherein said inner portion is made offlexible foamed polyethylene.
 11. A replacement disc for use betweenadjacent vertebrae comprising:an outer portion; and an inner portionsubstantially completely surrounded by said outer portion, said innerportion being made of a foamed material and being softer than said outerportion, said replacement disc being sized and shaped in substantiallythe form of a natural disc which is present between adjacent vertebraeto fit and be held between said adjacent vertebrae.
 12. The replacementdisc of claim 1 shaped in substantially the form of a natural disc whichis present between adjacent vertebra.